The 5 year survival rate for patients with pancreatic ductal adenocarcinoma (PDAC) has improved only marginally (3% -> 6%) over the past 35 years and despite considerable effort to develop therapeutics to treat PDAC, there has been a failure to significantly shift patient outcome. What is required are new, innovative and complementary approaches that better define the biology that drives disease initiation and that sustains tumor formation and progression so that improved treatments can be developed. PDAC is thought to initiate in acinar cells that acquire an activating mutation in the Kras protooncogene and that subsequently transition to a duct- like state by a process known as acinar-ductal metaplasia (ADM). Although ADM is a common feature of pancreatic cancer patients, there remains a critical gap in defining the transcriptional networks that are triggered by Kras mutation and that control the ADM -> PDAC pathway. The long-term goals of this study are to define the biological pathways that initiate and maintain advanced disease. The objective is to identify the transcriptional changes that are induced upon Kras activation and to test their importance to tumor development. The central hypothesis is that PDAC initiates from acinar cells via a phenotypic switch that requires silencing the acinar transcription program and activating a ductal transcription program. This hypothesis will be tested by pursuing two Specific Aims - (1) to identify acinar transcription networks that prevent acinar -> PDAC progression and (2) to establish how the ductal SOX9 transcription network drives ADM/PDAC development. These complementary aims will be accomplished using gain-of-function and loss- of-function strategies in inducible PDAC mouse models and in 3D culture systems that mimic the in vivo ADM response. The central transcription events instrumental in KRAS-induced ADM will be rigorously tested in human PDAC cells and in primary patient samples. The rationale for the proposed research is that these studies will be the first to probe the initial transcriptional changes in KRAS-expressing acinar cells and the first to manipulate these pathways in PDAC tumors. This contribution is significant because it will (i) define the earliest regulatory points n KRAS-induced PDAC, (ii) identify downstream genes that are regulated by duct transcription networks, and (iii) test if perturbation of specific gene targets can influence tumor development. The proposed research is innovative because it represents a departure from the status quo by approaching the disease from the earliest transcriptional events that guide the conversion of acinar cells to ductal preneoplastic lesions and by following these transcriptional networks in pancreatic tumors. The discoveries made will define the primary biological events associated with PDAC (the fourth leading cause of cancer deaths in the U.S.) and will direct future approaches aimed at testing new biomarkers and developing improved diagnostic and therapeutic tools to successfully treat patients suffering from this deadly disease.